Wells are used in the oil and gas industry to obtain fossil fuels and other fluids entrained in subterranean formations. Once a well is drilled, many types of equipment may be deployed in a well to perform tasks within the well, such as a perforating gun to detonate charges and create perforations through the wellbore and into the strata surrounding the wellbore to access the entrained natural resources, release or set a plug to obstruct a portion of the wellbore for isolation and further tasks, to apply materials to portions of the wellbore or well casing such as acid or cement, to perforate holes at specific locations of the wellbore or casing, or to activate a piece of remote equipment such as to provide signals, information, or log data in the wellbore or conditions at the downhole location. In these examples, precise location of the equipment within the well is critical to achieve optimal results, and in some cases, avoid dangerous conditions, such as from inadvertent detonation of a perforating gun too close to the surface. Despite the importance of precise location and safe activation, being able to determine the absolute and relative location of a piece of equipment within a wellbore and prevent inadvertent activation until the precise time or location needed still presents challenges.
For instance, in most settings, a wireline or slickline is used to lower the device downhole to the desired location. The most common way to determine the location of the device is by measuring from a surface device how much wireline or slickline has been sent down the wellbore. This is not always a reliable method of location determination, however, since the wireline or slickline may encounter obstacles in the wellbore, becoming snagged or wrapped around the obstacle before becoming freed for continued travel down the wellbore, or the surface cable length measuring devices could fail. Navigating the heel of a wellbore where it turns from a vertical orientation to a more horizontal orientation relative to the surface may also require releasing more wireline or slickline than corresponds to the distance traveled. Also, a wireline or slickline may be severed in the wellbore with or without knowledge of this occurrence at the surface where the line is being fed. In this case, the amount of line fed down the wellbore is entirely divorced from the location of the device being lowered.
Because of the many problems associated with using wireline or slickline, some devices have been developed for automatic or remote activation so a reference to the surface is not needed. However, these devices are rife with safety concerns. For instance, remote detonators for perforating guns are known, but they often rely on preset timers or pressure activation for detonation. Detonation is therefore based on calculations of where the perforating gun should be in the wellbore after a particular amount of time traveling at a particular speed, for example, but these are only calculations and may not accurately reflect the actual location of the perforating gun. For instance, the perforating gun may move slower through the wellbore than expected, such as from encountering an obstacle, or it may move faster than calculated. Not knowing the actual location of the perforating gun can result in perforations being made at unintended locations or even detonation dangerously close to the surface.
Efforts have been made to develop sensors that can provide locational information of a device. There are many different types of sensors, both active and passive, that have been used to determine the location of a piece of equipment within a wellbore. For example, U.S. Pat. Nos. 7,385,523 and 6,333,700 to Thomeer, et al. disclose the use of non-acoustic transponders affixed to the casing of a wellbore and a mobile tool, such as a perforating gun. The transponders emit identifying codes and communicate with one another when in proximity to each other. The perforating gun is fired when a transponder detects a matching code. The transponder types can include RFID recognizing unique identifying sequences or codes, magnetic pulse, magnetic field strength or polarity, magnetically encoded information, or optical transponders such as lasers detecting reflected patterns. Multiple transponders can be used at different locations along the well to permit the identification of the location of the tool. However, Thomeer requires only a single detection event to activate the tool. It provides no protection against accidental firing.
Similarly, U.S. Pat. No. 9,366,134 to Walton, et al. also discloses the communication between active transitory nodes on a movable tool and corresponding stationary nodes located in the wellbore to determine the position of the movable tool within the wellbore. Location of the tool may be determined as either absolute location by addressing stationary nodes, or relative location by counting nodes as they are passed. Various sensor types are disclosed, including temperature, pressure, magnetic fields, and fluid flow, all of which provide information on the conditions within the well. The tool, such as a perforating gun, is introduced into a wellbore in an inactive state, and is only turned to an active state upon reaching a certain depth or location. While the various sensors can be used to determine the location of the perforating gun before detonation, there is no safety mechanism to prevent accidental firing.
On the other hand, International Patent Application Publication No. WO 2015/118087 to Van der Ende discloses a system to avoid unintentional detonation of a perforating gun, such as from RF interference. The system uses information from various sensors provided to a code-activated switch at the surface to unlock the switch and create a safe firing window. Various sensors collect data on temperature, pressure, and time of the movement of the perforating gun, and transmit this data up a wireline to the code-activated switch at the surface. A key encrypted with physical and electronic settings must match the physical array of switches in the tool to unlock the system and permit firing of the device. However, no reference is made to absolute or relative positioning of the perforating gun, but rather focus is on the lockout mechanism which prevents accidental firing. Similarly, U.S. Pat. No. 6,273,187 to Voisin, Jr., et al. discloses a detonation system which detects pressure and temperature and uses a timer interlock to create a window for possible detonation. However, it does not determine the location of the device within the wellbore.
Therefore, there remains room for improvement for a way to determine the absolute and relative location of a device within a wellbore, and to coordinate this location information with a safety interlock system to prevent inappropriate activation or firing of the device when not at the desired location, all without reference or communication to the surface.
Like reference numerals refer to like parts throughout the several views of the drawings.